Recording sheet and means for mounting same on a rotary drum



Jan- 20, 1 J. M. CUNNINGHAM RECORDING SHEET AND MEANS FOR MOUNTING SAMEON A ROTARY DRUM 2 Sheets-Sheet 1 Original Filed June 6, 1952 INVENTOR.J4M5 M. (VA/A/WGAWM 1959 J. M. CUNNINGHAM 2,869,966

RECORDING SHEET AND MEANS FOR MOUNTING SAME ON A ROTARY DRUM OriginalFiled June 6, 1952 2 Sheets-Sheet 2 United States Patent Q RECORDINGSHEET AND MEANS FOR MOUNT- ING SAME ON A ROTARY DRUM James M.Cunningham, Encino, Califl, asisgnor to E. R. Chilcott and Doris C.Chilcott, a co-partnership doing business as Techno Instrument Company,Los Angeies,

Original application June 6, 1952, Serial No. 2%,104, now Patent No.2,806,757, dated September 17, 1957. Divided and this application August3, 1955, Serial No. 526,221

18 Claims. (Cl. 346-74) This invention relates to recording devices ofthe type wherein a recording medium in the form of a sheet is releasablymounted on a drum or cylinder, the invention being directed both to themounting means and to the sheet itself. While the invention is broadlyapplicable for its purpose, it has special utility as applied to amultiplechannel recorder for making a plurality of synchronous recordsfrom a plurality of signal sources on a single recording medium. Such amultiple-channel recorder may be employed, for example, in a geophysicalexploration procedure wherein seismic waves created by a test eX-plosion are detected at multiple terrain points for subsequent study andanalysis.

This application is a division of my copending application entitledMultiple-Channel Magnetic Recorder, Serial No. 292,104 filed June 6,1952, now Patent No. 2,806,757, issued September 17, 1957.

The broad object of the invention is to provide a mode of cooperationbetween a rotary drum or cylinder and a recording sheet that will permitthe recording sheet to be quickly and easily mounted in a positivemanner at an accurately predetermined position on the cylinder and to beas quickly and easily removed.

One of the more specific objects of the invention is to assure that themounted recording sheet overlies the peripheral surface of the drum in asmooth and snug manner under uniformly distributed tension. A specialproblem in this regard is to obtain the desired smoothness anddistribution of tension regardless of minor variations in di- 1 mcnsionamong successively used recording sheets. Variations in dimension areunavoidable in practice.

The present invention meets this problem by applying yielding force atnumerous points spaced across the width of the end of the recordingsheet with each yielding force acting independently of all the others.In this regard a feature of the invention is the concept of overlappingthe two ends of the sheet on the cylinder and of providing elongatedapertures or slots in the two ends of the sheet with the slotspositioned to overlap in a variable manner when the sheet is mounted onthe cylinder. With this arrangement the application of yielding force tospread the various overlapping slots results in placing the sheet underthe desired tension around the cylinder. The special advantage of thearrangement is that the slots may be so dimensioned and so positioned asto provide a range of adjustment sufficient to accommodate all minorvariables encountered in practice including both variations in thedimensions of successive sheets and variations in differ ent cylinderson which the sheets may be mounted.

A further problem is to provide means for mounting a sheet on thecylinder in the manner described that will not interfere with the travelof the sheet past the magnetic heads that are used both for recordingsignals on the sheet and for subsequently reproducing the signals. Theinvention meets this problem by providing a recess across the peripheryof the cylinderin the region where the 2 sheet ends overlap so that theoverlapping ends of the sheet may be offset inwardly into the recess.This arrangement permits the use of sheet-engaging means in the cylinderrecess inside the outer circumference of the cylinder, thus avoidingconflict with the magnetic heads that lie outside this circumference.

The various features, objects and advantages of the invention may beunderstood from the following description considered with theaccompanying drawings.

In the drawings, which are to be regarded as merely illustrative:

Fig. l is a sectional view of a portion of the apparatus that includesthe rotary drum and the associated magnetic heads;

Fig. 2 is an enlarged detail of Fig. 1 showing how a magnetic head ismounted on a holder;

Fig. 3 is a fragmentary section taken as indicated by the line 33 ofFig. 2;

Fig. 4 is a fragmentary section taken as indicated by the line 4-4 ofFig. 1;

Fig. 5 is a fragmentary sectional view showing one of the sheet engagingmeans in its release position;

Fig. 6 is an enlarged detail of Fig. l with the sheet engaging meansshown in dotted lines;

Fig. 7 is a section taken along the axis of the drum as indicated by theline 7-7 of Fig. 1;

Fig. 8 is a fragmentary section taken as indicated by the broken line8-8 of Fig. 1;

Fig. 9 is a fragmentary view taken as indicated by the arrow in Fig. 8,showing the index means for guidance in adjusting the magnetic heads;and

Fig. 10 is a fragmentary view of the periphery of the drum showing thesheet engaging means extending through the wall of the drum.

General arrangement The specific embodiment of the invention selected byWay of illustration is a multiple channel, magnetic recorder-reproducer,designed primarily for field service in making seismic recordings forgeographical exploration. This apparatus includes a rotary drum 25 onwhich is mounted a suitable recording medium in the form of a flexiblesheet to be moved by the drum in a curved path of travel past arecording zone.

A bank or row of holders 2-6 for supporting magnetic heads in this zoneis positioned relatively close to the periphery of the rotary drum,there being one holder 26 for each channel. In this preferred practiceof the invention, the holders 26 are thin bars or blade-like membersmounted edgewise with respect to the drum 25 and as many as forty-foursuch holders may be employed for simultaneously recording as many trackson the magnetic sheet medium. Usually one of the tracks will be used fora timing record.

Rotary drum and driving mechanism As best shown in Fig. 7 the rotarydrum 25 comprises a cylindrical wall 4b supported by two circular endwalls 41, each of the end walls having a hub portion 42. A suitableshaft 45 extending through the hub portions 42 and attached thereto bysuitable screws 46 is journaled in suitable anti-friction bearings 47.The bearings 47 are mounted in a pair of vertical support plates 48 thatare suitably attached to the base plate 21 by screws 49.

The rotary drum 25 may be actuated in any suitable manner, for example,by a synchronous motor in the motor housing. For this purpose the shaft45 extends into the motor housing and carries a relatively large pulley54 adapted to be actuated by an endless string belt 55. The string belt55, which is maintained taut by an idler pulley 56 on a spring loadedarm 57, is actuated by a drive pulley 53. The drive pulley 58 is on adrive 3 shaft on, driven by suitable reducing gearing (not shown) in agear case at. The motor is connected with the gearing by a motor shaftoZ'that carries a suitable flywheel es.

Preferably suitable braking means is included to stop the rotary drumimmediately upon de-energization of the motor. This braking means may beof a well-known magnetic type which is normally spring actuated forbraking effect and is electrically retracted to free the rotary drumfrom the motor. it is contemplated that the electrically retractablebrake will be in t same circuit as the motor so that the brake will beat ornatically retracted whenever the motor is energized and willautomatically stop the rotary drum immediately upon deenergization ofthe motor.

While any suitable recording medium in sheet for may be em loyed, thepresently preferred m n j t powder-coated plastic sheet of the sameconstruction as conventional magnetic tape. A recording sheet wrappedaround the periphery of the rotary drum 25 suffices for the presentpurpose of geophysical exploration since the maximum recording periodrequired for seismic wave recording in geophysical exploration is lessthan 6 seconds and a drum 7 /2 inches in diameter recording at 21peripheral speed of 3 /2 inches per second will make less than onecomplete revolution in 6 seconds. in the present preferred practice ofthe invention, the recording medium is in the form of a powder-coatedplastic sheet 11% inches wide by 24% inches long which is wrappedlengthwise around the drum and is releasably attached thereto.

Sheet-attachment means While the recording sheet may be releasablymounted on the rotary drum ZSby various expedients, a feature of thepresently described preferred embodiment of the in vention is theconcept of employing recording sheets having suitable apertures in theirtwo end portions with suitable sheet-engaging means built into theconstruction of the rotary drum 2% for cooperation with the sheetapertures. ft is contemplated that the apertures at each end of a sheetwill overlap on the rotary drum 25 in such manner that thesheet-engaging means may extend through the overlapping apertures andexpand against the edges of the apertures thereby to place the sheetunder longitudinal tension at a plurality of points.

This method of releasably securing a flexible recording sheet around adrum may be understood in principle by referring to Figs. 5, 6 and 10. Aflexible recording sheet generally designated '79 is wrapped on theperiphery of the rotary drum 25 with one end portion 73 of the sheetoverlapping the second end portion 74. These two end portions 73 and idof the sheet 7t) have pluralities of slots which match so that majorportions of the pairs of slots overlap. It is important to note thatonly the outer end portions of the two slots overlap in the finalposition of the sheet f ll. Thus in Fig. 6 showing the overlapping ends73 and 7a in their final positions, the outer end or edge 75 of a slot"/5 in the end portion 73 overlies the corresponding slot 77 in theother end portion 74 and the outer end or edge of the lower slot 77underlies the upper slot 79. The other ends of the two slots are not inoverlapping relationships. Thus a suitable means extending into the twoslots and expanded longitudinally of the slots will engage the endportions '73 and 7d of the two slots to place the sheet under tensionwithout interference by the inner ends of the slots.

Any suitable sheet-engaging means may be employed for this purpose ineach pair of slots but preferably such means comprises a pair of movablefingers ill) shown in dotted lines in Pig. 6. it will be noted in Fig.6, where the two fingers 3d are spread apart to place the sheet 75 undertension, one finger abuts the outer end portion '75 of the upper slotand the other finger abuts the outer end 75% of he lower slot '77.

A further feature of the preferred practice of the invention is the factthat the sheet-engaging fingers 80 lie wholly within the outercircumference of the sheetwrapped drum so that the sheet-engagingfingers may be out of range of magnetic heads that are positioned ad- 5jacent the drum to contact the outer surface of the wrapped sheet. Toprovide this feature the cylindrical wall 4% of the rotary drum 25 has asuitable longitudinal groove or recess 81 to receive the overlappingsheet ends 73 and 74 and is further provided with a plurality oflongitudinal slots 82 arranged in a row along the groove Thesheet-engaging fingers 80 extend out through the drum slots 82 butterminate short of the circumference defined by a sheet on the drum.

In the preferred construction of the invention the sheet-engagingfingers 89 are notched or otherwise formed to provide end flanges 85 toengage the outer surface of the sheet 7%, the two end flanges being ofdifferent thicknesses as shown in Fig. 5 since one end flange engagesthe outer end portion of the sheet and the other end 20 flange engagesthe inner underlying edge portion of the sheet. Preferably all of thepairs of sheet-engaging fingers 81) are manually controlled in unison tocontract for the purpose of engaging a sheet and to expand for thepurpose of placing the sheet under tension.

25 The pairs of sheet-engaging fingers till may comprise the outer endsof pairs of cooperating levers generally designated 86 and best shown inPig. 5. Each lever 86 of a pair has a cylindrically curved surface 37 toslidingly engage a longitudinal pivot rod 83 for rotary movement aboutthe axis of the rod. As best shown in Fig. 7, the rod 38 is mounted inthe end walls 41 of the rotary drum and is formed with spacedcircumferential grooves 39 to receive the pairs of levers 86. The innerends of each pair of the levers 86 straddle a rocker shaft 96 which iscut away longitudinally to provide an extensive cam portion E l. Asshown in Fi 5 the cam portion 91 is relatively narrow along onecross-sectional dimension. A suitable spring $4 having hooked ends 95interconnects the two levers 86 to draw the two lovers together therebyat) holding the two levers in engagement with the pivot rod 38.

in m) the released position of the two levers on wherein the two fingersare contracted together hown in .Frg. S, the rocker shaft 9% is rotatedto a position at 43 which the cam portion 91 of the shaft spreads thelower portions of the two levers apart in opposition to the spring Whenthe rocker shaft ill is rocltcd 90 as shown in Fig. l the cam portion 91of the rocker shaft p rmits the spring to draw the two levers of each aair together at their lower ends thereby to spread the ugers apart intoyielding engagement with the two -nds of the sheet l'tl as heretoforedescribed. The pivot d 8% acts as a fulcrum for the two levers and thecnsion of the spring 9 5 in urging the two sl'iectengaging 55 ringers8ft apart is transmitted to the sheet '73.

The rocker shaft may be manually controlled in any suitable manner. Inthe constr' .tion shown. for example, the rocker shaft extends throughone of the end walls 41 of the rotary drum 2S and ionrnaied in the noend walls for rocking action. A suitable actuate ing arm 1% is mountedon the outer end of the rocker shaft 5 by a suitable screwfill. Theactuatil n tilt;

is relatively thin as shown in Fig. 7 for one not: in the clearancespace between the rotary drum (2.: a the ade5 jacent support plate 43and serves as convent t firmer ece for moving the rocker shaft bet eculZS two posh trons.

Since the pairs of levers together with the pivot rod and the rockershaft 9% tend to throw-x the rotary drum off balance the end walls ofthe row J drum are preferably formed with thickened portions 553 2 (Fig.

7) to serve as counterweights to balance the drum.

Mounting means for the magnetic heart's K5 "the preferred practice ofthe invention contemplates the employment of ring-type magnetic heads105 which are specially designed for compactness in axial dimension. Themagnetic heads 105 are closely spaced in a row across the periphery ofthe rotary drum 25, the row being aligned transversely orperpendicularly of the direction of travel of the recording sheet 70.While any suitable means may be provided for supporting the magneticheads 1% in such a recording zone, the preferred practice of theinvention is characterized by the use of holders 26 in the form of blademembers as heretofore stated. As best shown in Fig. 2 the row of spacedbladelilre holders 26 lie relatively close to the recording sheet 70 onthe rotary drum 25 and the individual holders are of curvedconfiguration. To provide space for the magnetic heads 105 the holders26 are cut away at their inner edges to provide ample recesses 107 thusproviding ample space for the row of magnetic heads 105.

Preferably the magnetic heads 105 are supported from the correspondingholders 26 by suitable mounting means that permit individual adjustmentof the heads with respect to the periphery of the recording sheet 70 onthe rotary drum. As best shown in Figs. 2, 3 and 4, each magnetic head105 is mounted for this purpose on a thin arm that extends into a space111 between two of the holders 26 and is pivotally mounted on one of theholders by a suitable pivot stud 112. In the region of the pivot stud112 each of the mounting means or arms 1113 is formed with an amplebearing portion 113 that is in intimate sliding contact with the face ofthe corresponding holder 26, the purpose of such construction being tohold the magnetic head 105 accurately to a predetermined arc ofadjustment relative to the rotary drum. Between the bearing portion 113and the corresponding magnetic head 165, the mounting arm 110 ispreferably relatively thin.

Preferably adjustability of the magnetic head 1G5 with reference to therotary drum is provided by an adjustment screw 115 in cooperation with asuitable wire spring 116. The wire spring 116 has one end 117 seated ina suitable small bore in the holder 26 for anchorage and is bent arounda stud 118 on the holder to press against the mounting arm 11ft. Theadjustment screw 115 has an eccentric head as may be seen in Fig. 4 sothat rotation of the screw in abutment with the mounting arm 11f) variesthe pivotal position of the mounting arm. Preferably the adjustmentscrew 115 is rotated to a position to permit the magnetic head tocontact the sheet 7ti on the rotary drum 25 but not to permit themagnetic head to touch the peripheral surface of the drum in the abenceof a sheet 70.

Preferably relative movement between each magnetic head 1615 and thecorresponding holder 26 is limited to the adjustment described andadditional adjustment of each magnetic head with respect to thedirection of travel of the recording sheet 71) is accomplished by bodilymovement of the holder 26 that carries the head. For this purpose, eachof the holders 26 is longitudinally movable in an arcuate path ofadjustment concentric to the rotary drum 25. It is contemplated thateach holder 26 will be slidably mounted in a suitable slot in a suitablesupport means with the slot serving as a guide channel for thelongitudinal adjustment movement of the holder.

In the present embodiment of the invention the bladelike holders 26 aresupported by two spaced transverse support members 121, each of whichextends between the two vertical support plates 48 and is fixedlyattached thereto by a suitable screw 122 and a pair of dowels 123 asshown in Figs. 8 and 9. Each of the support members 121 has a row ofopenings or slots 125 each of which has an arcuate bottom surface 126concentric to the rotary drum 25. Each of the holders 26 has an endportion 127 at each of its ends to slidingly extend into the slots 125of the two support members 121. The two end portions 127 have arcuateedge surfaces 12% that are also of concentric curvature for slidingcontact with the arcuate bottom surfaces of the slots 125. By virtue ofthis arrangement the various holders 26 may be slidingly adjustedlongitndinally in the slots of the two support members 121 and will beguided by the slots concentrically with respect to the rotary drum 25.

Any suitable means may be provided to slidingly retain the holders 26 inthe slots 125 and to hold the holders individually at adjustedlongitudinal positions in the slots. Preferably, the holders 26 areyieldingly pressed into sliding contact with the arcuate bottom surfacesof the slots and are yieldingly urged longitudinally against adjustablestops to fix their longitudinal positions.

The yielding means to retain the holders 26 in the slots in pressurecontact with the arcuate bottom surfaces 126 of the slots may comprisesuitable leaf springs 13% best shown in Figs. 8 and 9. Each of the leafsprings 13ft is secured to one of the support members 121 by a suitablescrew 131 and is formed with a pair of arms 132 each of which pressesinward on one of the holders 26. As may be seen in Fig. 1 both of thesupport members 121 are provided with leaf springs so that each of theholders 26 is pressed inward by a leaf spring arm 32 at each end of theholder.

The yielding means to urge each holder 26 in one longitudinal directionmay comprise a suitable Wire spring 135 having one end 136 inserted inthe holder for anchorage, the wire spring being wrapped around a stud137 on the holder in such manner as to press against the adjacentsupport member 121 and thereby tend to urge the holder longitudinallydownward as viewed in Fig. 1.

The upper end of each holder 26 is provided with a suitable stop screw140 which is in adjustable abutment with the upper support member 121,as shown in Fig. 1, to hold the holder at any desired longitudinalposition in opposition to the pressure of the wire spring 125. Eachscrew 14% has a knurled head 141 for convenient manual rotation and ismounted in a flange 142 on the end of the holder, which flange overhangsthe support member 121. In the construction shown, each flange 142 isprovided by mounting an angular clip 142 on the end of the holder 26. Afeature of the invention is the concept of positioning the angular clips143 and the corresponding adjustment screws 140 in two rows with thesuccessive screws staggered.

A suitable index means may be provided for guidance in manipulating thescrews 14% for longitudinal adjustment of the individual holders 26.Such index means may be provided in any suitable manner and may besuitably calibrated. Fig. 9 shows, by way of example, an indexarrangement that may be used to advantage for adjusting the holders 26longitudinally to compensate for various distances of wave travelthrough the earth from a wave propagating point to various detectorscorresponding to the channels of the apparatus.

The index arrangement includes a Zero reference line 145 scribed on theupper support member 121 to intersect the row of slots 125. Each of theholders 26 is scribed with a corresponding reference line 1 56. When allof the adjustment screws 140 are manipulated to make all of thereference lines 146 on the various holders register with the zeroreference line 145, all of the magnetic heads are accurately positionedfor synchronous recording of wave signals arriving simultaneously atdetectors corresponding to the magnetic heads. Since the signal wavesmust travel various distances through the earth to reach the variousdetectors the signals do not arrive at the detectors simultaneously andtherefore synchronous recording in the sense of geometrical simultaneityof the recorded signal components on the sheet 76 will requirecompensating longitudinal adjustment of the holders 26.

For guidance in such adjustment the zero reference line 145 on thesupport member 21 is part of a scale that extends in both directionsfrom the zero reference line as may be seen in We The scale iscalibrated Operation of the apparatus The operation of the describedmultiple-channel magnetic recorder may be readily understood from theforegoing description. It is a simple matter to swing actuating arm tothe position shown in to contract the two sheet-engaging fingers thedrum slots 82. A recording sheet "It? is then wrapped around the drumand the overlapping slots 73 and 74- at the ends of the sheet areslipped over the ends of the contracted lingers 3h. Throwing theactuating wi from the position shown in Fig. 5 to the pa shown in Fig. 1rotates the cam 91 to permit the spr 9d of the various pairs of levers86 to move the finger hi3 apart and this expanding action on the part ofeach pair of fingers it results in placing the sheet 76; in iongitudinaltension at a plurality of spaced points across the rotary drum. In thismanner the sheet 70 is stretched smooth against the peripheral surfaceof the rotary drum.

The various screws i itl are manipulated for longitudinal adjustment ofthe individual holders 26 to provide the desired phase synchronizationof the multiple tracks on the recording sheet id.

When the apparatus is readied for operation, steps are taken to createthe desired seismic waves by detonation and the motor is energized torotate the drum At the end of the short recording period as the rotarydrum approaches completion of one rotation the motor is deenergized andthe brake automatically stops the rotary drum.

it is usually desirable to switch the magnetic heads 1 immediately intoreproducing circuits for reproduction the recorded signals to make surethat proper recordi g has been accomplished. Once the recording has beenchecked in this manner the sheet 76 may be removed from the drum andfiled for further study.

The complete record sheet may be filed in the convenient and compactmanner of a sheet of paper and pro-- vides a permanent record notsubject to deterioration nor vulnerable to damage in the course ofordinan handling. it is especially advantageous that the recording ofthe multiple signals is reproducible immediately at the end of therecording period. if desired, the recorded signals may be analyzed onthe spot and to this end the signals may be fed to a suitable electronicanalyzer and electronic filters may be employed for selective study ofsignificant components of the signals.

My description in specific detail of a preferred practice of theinvention will suggest to those skilled in the art various changes,substitutions and other departures from my illustrative disclosure thatproperly lie within the spirit and scope of the appended claims.

1 claim:

1. in a device of the character described, the com bination of: a rotarydrum having a generally cylindrical external surface and a longitudinalperipheral recess; a magnetic recording medium in the form of a sheetwrapped around said drum with the ends of the sheet overlapping at saidrecess, said overlapping ends having a plurality of pairs of aperturespositioned along the complete length of said overlapping ends, saidpairs of apertures overlapping at their outer ends; a plurality ofmagnetic recording heads mounted in a position contiguous to theexternal surface of said drum and along its length; means to urge saidmagnetic recording heads t said recording medium; and a plurality ofsheet-enga means carried by said drum and extending outwa'o said recessinto said pairs of apertures respectively, sa sheet-engag ng means beingadapte to retractably era pand in pairs of overia ping apertures toplace said seas sheet under tension, said. -engaging n sans being p0-sitioned generally within the cylindric 1 external surface of said drumand having circumferentially extending flanges to hold said sheet endson said sheet-engaging member and Within said recess.

2. A rotary drum set forth in claim 1 which in cludes yielding means toexpand said sheet-engaging means thereby to yieldingly tension saidsheet.

3. A rotary drum as set forth in claim 2 which in cludes manuallyoperable n. s to contract said sheetmeans in unison in opposition tosaid yielding ciiga means.

A rotary drum as set forth in claim 3 in which each of saidsheet-engaging means comprises a pair of pivoted members and yieldingmeans cooperative therewith to urge said pivoted members apart.

5. A combination as set forth in cla manually operable means iscontrolled member at one end of the drum.

6. in a device of the character described, a rotary drum to carry arecording medium in the form of a sheet wrapped around the drum with theends of the sheet overlapping, said overlapping ends having pluralitiesof apertures positioned along the complete length of said overlappingends, said apcrtt es being positioned and dimensioned to overlap attheir on ends when the sheet is on the drum, said drum having aperipheral recess to permit the overlapping ends of the sheet to beflexed inside the outer circumference of the drum; a plurality ofmagnetic recording heads moun in p sition contiguous to the cylindricalexternal Bull of said drum and along its length; means to urge saidmagnetic recording heads against said rccoriing medium; pairs of pivotedfingers extending outward iron. the interior of the drum into said'ecess but not beyond the outer circumference of the drum to engagerespectively the pairs of overlapping apertures of the sheet, said a sohaving circumferenim 4 in which said by an operating to urge the fingersof each of said pairs apart thereby to place said sheet under tension;manually operable means to contract said pairs of fingers tosheet-releasing positions.

7. in a device of the chara biuation of: a rotary drum n Jl a generallycylindrical surface and a lougit al peripheral recess; a magneticrecording medium in the form of a sheet Wrapped around said drum withthe ends of the sheet overlapping at said recess, said overlapping endshaving a plurality of pairs of apertures overlapping at their outerends; a plurality of magnetic recording heads mounted in a positioncontiguous to the external surface of said drum and along its length;means to L" said magnetic recording heads against said recording ledium, d heads being movable back and forth to accommodate unevenness insaid record or eccentricity in said dru a plurality of sheetcngagingmeans carried by said drum extending outwardly at sai. recess into saidairs of apertures respectively, said sheet-engaging means being adaptedto retractably errand in said pairs of overlapping apertures to placesai ret under to and stop means to prevent said n. etic recordin dsirorn touching said sheet-engaging m cter described, the comit the terdescribed, a rotary indium in the form of a drum with the ends of theing ends having pluralities cnsioned to overlap at of aperturespositioned their outer ends when the s fingers pivoted from about anaxis longitudinally through said drum, said fingers extending outwardlyfrom the interior of the drum to project through respective pairs ofoverlapping apertures of the sheet; yielding means to urge the fingersof each of said pairs apart thereby to place said sheet under tension,each corresponding pair of fingers being free to rotate about said axisindependently of any other corresponding pair when said yieldingmeans'is operative; and manually operable means to contract said pairsof fingers to render said yielding means inoperative and thereby toplace the sheet-engaging ends of said fingers together.

10. The invention as defined in claim 9, wherein said sheet-engagingmeans is positioned generally within the external surface of said drumhaving circumferentially extending flanges to hold said sheet ends onsaid drum within said recess.

11. The invention as defined in claim 10, wherein said manually operablemeans is a shaft having a cam for each of said fingers, said cam havinga small and large diameter to fit between ends of said fingers oppositetheir sheet-engaging ends and on the opposite side of said axis.

12. The invention as defined in claim 11, wherein said drum and thesheet-engaging ends of said fingers are both recessed longitudinallyalong the length of the drum, wherein a plurality of magnetic recordingheads are mounted in a position contiguous to the external surface ofsaid drum and along its length; wherein resilient means are provided tourge said magnetic recording heads against said recording medium, saidrecording heads having freedom of movement toward and away from saiddrum; and wherein stop means are additionally provided to prevent saidrecording heads from touching said fingers.

13. In recording and reproducing apparatus, the combination comprising:a generally cylindrical drum; a record sheet wrapped around said drumwith its ends overlapping, said overlapping ends having at least a pairof apertures overlapping only at their outer ends; a pair of fingerspivoted from about an axis extending generally longitudinally throughsaid drum, said fingers extending outwardly from the interior of saiddrum to project through said overlapping apertures; yielding means tourge the outer ends of said fingers apart to place said record sheet intension, both of said fingers being free to rotate about said axis tohold said record sheet in the position it was originally wrapped aroundsaid drum; and means for contracting the outer ends of said fingers torender said yielding means inoperative.

14. In recording and reproducing apparatus, the combination comprising:a generally cylindrical drum; a record sheet wrapped around said drumwith its ends overlapping, said overlapping ends having at least a pairof apertures overlapping only at their outer ends; a pair of fingerspivoted from about the same axis, extending generally longitudinallythrough said drum, said fingers extending outwardly from said axis inthe interior of drum to project through said overlapping apertures,fingers also extending inwardly in the drum beyond said axis; resilientmeans connected to the inner ends of said fingers to urge the outer endsof said fingers apart to place said record sheet in tension; and meansto contract the outer ends of said fingers to render said yielding meansinoperative.

15. The invention as defined in claim 14, wherein said means to contractsaid fingers includes a shaft and a cam on said shaft having a small andlarge diameter to fit between the inner ends of said fingers.

16. In recording and reproducing apparatus, the combination comprising:a generally cylindrical drum; a record sheet wrapped around said drumwith its ends overlapping, said overlapping ends having a plurality ofmore than two pairs of apertures overlapping only at their outer ends; apair of fingers for each of said pair of overlapping apertures pivotedfrom about an axis extending generally longitudinally through said drum,each of said pair of fingers extending outwardly from the interior ofsaid drum to project through a corresponding pair of overlappingapertures; yielding means to urge the outer ends of said fingers apartto place said record sheet in tension; and means for contracting theouter ends of said fingers to render said yielding means inoperative.

17. In recording and reproducing apparatus, the combination comprising:a generally cylindrical drum; a record sheet wrapped around said drumwith its ends overlapping, said overlapping ends having a plurality ofpairs of apertures overlapping only at their outer ends; a pair offingers for each of said pair of overlapping apertures pivoted fromabout an axis extending generally longitudinally through said drum, eachof said pair of fingers extending outwardly from the interior of saiddrum to project through a corresponding pair of overlapping apertures;yielding means to urge the outer ends of said fingers apart to placesaid record sheet in tension; and means for contracting the outer endsof each of said pairs of fingers simultaneously to render said yieldingmeans inoperative.

18. The invention as defined in claim 17, wherein said means to contractsaid fingers includes a shaft and a cam on said shaft for each of saidpairs of fingers, each cam being disposed in the same angular positionon said shaft and having small and large diameters to fit between innerends of said fingers.

said said References Cited in the file of this patent UNITED STATESPATENTS 1,531,124 Murray Mar. 24, 1925 2,109,152 Meisel Feb. 22, 19382,729,453 Camras Jan. 3, 1956

